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On 2017-09-21 10:01, Dietmar Rieder wrote:
Hi, I'm in the same situation (NVMEs, SSDs, SAS HDDs). I asked the same questions to myself. For now I decided to use the NVMEs as wal and db devices for the SAS HDDs and on the SSDs I colocate wal and db. However, I'm still wonderin how (to what size) and if I should change the default sizes of wal and db. Dietmar On 09/21/2017 01:18 AM, Alejandro Comisario wrote:
But for example, on the same server i have 3 disks technologies to
deploy pools, SSD, SAS and SATA.
The NVME were bought just thinking on the journal for SATA and SAS,
since journals for SSD were colocated.
But now, exactly the same scenario, should i trust the NVME for the SSD
pool ? are there that much of a gain ? against colocating block.* on
the same SSD?
best.
On Wed, Sep 20, 2017 at 6:36 PM, Nigel Williams
<nigel.williams@xxxxxxxxxxx <mailto:nigel.williams@xxxxxxxxxxx>> wrote:
On 21 September 2017 at 04:53, Maximiliano Venesio
<massimo@xxxxxxxxxxx <mailto:massimo@xxxxxxxxxxx>> wrote:
Hi guys i'm reading different documents about bluestore, and it
never recommends to use NVRAM to store the bluefs db,
nevertheless the official documentation says that, is better to
use the faster device to put the block.db in.
Likely not mentioned since no one yet has had the opportunity to
test it.
So how do i have to deploy using bluestore, regarding where i
should put block.wal and block.db ?
block.* would be best on your NVRAM device, like this:
ceph-deploy osd create --bluestore c0osd-136:/dev/sda --block-wal
/dev/nvme0n1 --block-db /dev/nvme0n1
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My guess is for wal: you are dealing with a 2 step io operation so in case it is collocated on your SSDs your iops for small writes will be halfed. The decision is if you add a small NVMEs as wal for 4 or 5 (large) SSDs, you will double their iops for small io sized. This is not the case for db.
For wal size: 512 MB is recommended ( ceph-disk default )
For db size: a "few" GB..probably 10GB is a good number. I guess we will hear more in the future.
Maged Mokhtar
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